A colorless, odorless gas ($N_2O$) inhaled through a small nasal mask. It is a mild sedative that induces a state of relaxation and euphoria, commonly known as "Laughing Gas."
It is the safest form of sedation, ideal for children or patients with mild anxiety. Unlike oral sedation pills, the effects wear off within minutes of breathing pure oxygen, allowing patients to drive themselves home.
Yes, it has a very high safety margin and is non-allergenic.